Posi-RAM™ Metabolite Detector

Description

With more and more sophisticated nuclear medicine applications, positron (ß+) counting has become of increasing interest. Positrons are unique in that their lifetime is measured in picoseconds. Once they interact with a nearby electron, they give rise to two directly-opposed 511 KeV gammas (“annihilation radiation”), one or both of which then may be counted with a conventional gamma counter. Today, 11C and 18F are the ß+-emitters of greatest interest. Produced at high activity levels with a cyclotron, their relatively short half-lives – 11C (t½ = 20.4 min), 18F (t½ = 110 min) – necessitate fast chemical processing and almost instantaneous utilization.

As production methods have improved, and with chemistry automated, it has become possible to rapidly synthesize and employ more complex molecules. The natural progression has then been to study metabolism. With the time for synthesis, the time within the biological system, the time for metabolite isolation, and the short half-lives, low-level ß+-counting is suddenly a requirement. The Posi-RAM™ has been developed specifically for that need.

The Posi-RAM is a coincidence counter based upon the same electronics platform employed in our ß-RAM detectors. Two opposed 1” x 1” BGO crystal photomultiplier assemblies sandwich a flat thin-wall cell coil. With the separation between the crystals < 0.2”, the geometric efficiency for collecting the annihilation gammas, one in each assembly, is quite high. At the same time, backgrounds are inherently low since only coincidences are recorded; PMT noise and conventional gamma counter backgrounds are rejected.

The Posi-RAM is a complete counter and is as suitable for gamma measurement as it is for positrons. It has two counting channels and a digital display. A built-in collector valve at the cell exit responds to manual or automatic control. There are digital and analog outputs. Laura software is available to perform decay correction, to automatically find and integrate peaks, and to control fraction collectors and auto-injectors.

On special order, the detector and electronics can be housed in separate cabinets.